Control system of internal combustion engine

ABSTRACT

A control system of an internal combustion engine in which a catalyst device having oxidation ability is arranged in the exhaust system, is provided. When a temperature of the catalyst device is lower than a set temperature, the combustion temperature is made a first combustion temperature or under or is made a second combustion temperature or over, to make an amount of lower olefin in the exhaust gas smaller than that when the combustion temperature is higher than the first combustion temperature and is lower than the second combustion temperature. Therefore, an amount of lower olefin which reduces the oxidation rate of CO in the catalyst device is decreased so as to realize the quick warming-up of the catalyst device by using of the oxidation reaction heat of CO.

TECHNICAL FIELD

The present invention relates to a control system of an internalcombustion engine.

BACKGROUND ART

To purify HC and CO in exhaust gas, an oxidation catalyst device or athree-way catalyst device is arranged in an engine exhaust system. Sucha catalyst device having the oxidation ability does not activatesufficiently in a low temperature condition like immediately after thestarting-up of the engine. It is desired for the catalyst device to bewarmed up quickly to an activation temperature in order to increase thepurification ability of HC and CO.

In the catalyst device having the oxidation ability, CO can be oxidizedat a lower temperature than that at which HC can be oxidized. Therefore,first, the oxidation reaction heat of CO raises the temperature of thecatalyst device. Incidentally, it is known that HC obstructs theoxidation of CO and therefore, the smaller the amount of coexisted HC,the more the oxidation rate of CO can be increased.

It has been suggested that a HC adsorption device is arrangedimmediately upstream the catalyst device (for example, refer toInternational Publication WO 00/27508). Accordingly, an amount of HCcoexisting with CO in the catalyst device can be reduced by theadsorption of HC in the HC adsorption device.

DISCLOSURE OF THE INVENTION

Even if the HC adsorption device is arranged immediately upstream thecatalyst device as mentioned above, in an engine operating state, theoxidation rate of CO cannot be increased very much and the quickwarming-up of the catalyst device cannot be realized.

Accordingly, an object of the present invention is to provide a controlsystem of an internal combustion engine, which can sufficiently increasethe oxidation rate of CO in a catalyst device having the oxidationability to realize the quick warming-up of the catalyst device.

A control system of an internal combustion engine in which a catalystdevice having the oxidation ability is arranged in the exhaust system asset forth in claim 1 of the present invention is provided, characterizedin that when a temperature of the catalyst device is lower than a settemperature, the combustion temperature is made a first combustiontemperature or under or is made a second combustion temperature or over,to make an amount of lower olefin in the exhaust gas smaller than thatwhen the combustion temperature is higher than the first combustiontemperature and is lower than the second combustion temperature.

A control system of an internal combustion engine as set forth in claim2 of the present invention is provided as the control system of aninternal combustion engine as set forth in claim 1 characterized in thatan engine operating area in which the combustion temperature becomeshigher than the first combustion temperature and lower than the secondcombustion temperature is set, and when the temperature of the catalystdevice is lower than the set temperature, it is prohibited that theengine operates in the engine operating area.

A control system of an internal combustion engine as set forth in claim3 of the present invention is provided as the control system of aninternal combustion engine as set forth in claim 2 characterized in thatthe worse the combustion is, the more the engine operating area isexpanded to the high engine load side.

According to the control system of an internal combustion engine as setforth in claim 1 of the present invention, when a temperature of thecatalyst device having the oxidation ability, which is arranged in theengine exhaust system, is lower than a set temperature, a combustiontemperature is made a first combustion temperature or under or is made asecond combustion temperature or over, to make an amount of lowerolefin, which particularly reduces the oxidation rate of CO, in theexhaust gas smaller than that when the combustion temperature is higherthan the first combustion temperature and is lower than the secondcombustion temperature. Therefore, the oxidation rate of CO issufficiently increased so as to realize the quick warming-up of thecatalyst device.

According to the control system of an internal combustion engine as setforth in claim 2 of the present invention, in the control system of aninternal combustion engine as set forth in claim 1, an engine operatingarea in which the combustion temperature is higher than the firstcombustion temperature and lower than the second combustion temperatureis set, and when the temperature of the catalyst device is lower thanthe set temperature, it is prohibited that the engine operates in theengine operating area. Therefore, the combustion temperature can beeasily made the first combustion temperature or under or made the secondcombustion temperature or over.

According to the control system of an internal combustion engine as setforth in claim 3 of the present invention, in the control system of aninternal combustion engine as set forth in claim 2, the worse thecombustion becomes, the more the engine operating area is expanded tothe high engine load side due to the lowering of the combustiontemperature. Therefore, even if the combustion deteriorates, thecombustion temperature can be certainly made the first combustiontemperature or under or made the second combustion temperature or over.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the exhaust system of an internalcombustion engine which is controlled by a control system according tothe present invention.

FIG. 2 is a time-chart showing changes of the oxidation rate of CO in anoxidation catalyst device.

FIG. 3 is a graph showing a relationship between a combustiontemperature and a concentration of lower olefin in the exhaust gas.

FIG. 4 is a first flow-chart showing a control of the engine by thecontrol system according to the present invention.

FIG. 5 is a second flow-chart showing a control of the engine by thecontrol system according to the present invention.

FIG. 6 is a map showing an area in which the engine operation isprohibited in the second flow-chart.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic view showing the exhaust system of an internalcombustion engine which is controlled by a control system according tothe present invention. In the figure, reference numeral 1 is an exhaustpassage and reference numeral 2 is a three-way catalyst device or acatalyst device having the oxidation ability with a honeycomb-shapedbase material on which at least an oxidation catalyst such as platinumis carried (including a NO_(x) storing/reducing catalyst device). Theengine may be a spark-ignition engine or a diesel engine.

Reference numeral 3 is a HC adsorption device arranged upstream thecatalyst device 2. The HC adsorption device 3 comprises ahoneycomb-shaped base material on which a beta zeolite or ZMS-5 iscarried. The lower the temperature of the device, the larger an amountof HC that can be adsorbed becomes. Therefore, the HC adsorption deviceadsorbs HC in the exhaust gas in low temperatures and releases theadsorbed HC in high temperatures.

The catalyst device 2 oxidizes HC and CO in the exhaust gas to purifythem. However, when the oxidation catalyst has not become an activationtemperature, the catalyst device cannot sufficiently oxidize particularHC and thus it is needed to quickly warm up the catalyst deviceimmediately after the engine starting-up. The catalyst device 2 canoxidize CO at a lower temperature than that at which HC can be oxidized,and thus is warmed up by using of the oxidation reaction heat of CO atthe beginning.

FIG. 2 is a time-chart showing changes of the oxidation rate of CO inthe catalyst device 2. The solid line shows a case of an exhaust gascontaining about 1600 ppm of propylene C₃H₆ (lower olefin) and CO inwhich the mixing of propylene is stopped at a time t0. The dotted lineshows a case of an exhaust gas containing about 1600 ppm of decaneC₁₀H₂₂ (higher olefin) and CO in which the mixing of decane is stoppedat the time t0. If HC does not coexist, the oxidation rate of COincreases to about 100%. However, because propylene or decane coexist,each oxidation rate of CO becomes lower than 100%. When the mixing ofpropylene or decane is stopped, each oxidation rate of CO graduallyincreases.

As shown in FIG. 2, the lower olefin of which carbon atom number is 5 orunder (for example, ethylene or propylene) obstructs the oxidation of COin the oxidation catalyst more than the higher olefin (decane) and thusdrops the oxidation rate of CO so much.

FIG. 3 is a graph showing a relationship between a combustiontemperature T (maximum combustion temperature) in the cylinder and aconcentration C of lower olefin in the exhaust gas. The concentration oflower olefin is largest at the combustion temperature TP (for example,about 1000K). When a combustion temperature T is this combustiontemperature TP or is higher than a first combustion temperature T1 (forexample, about 900K) and lower than a second combustion temperature T2(for example, about 1100K), the concentration of lower olefin becomesrelatively high and a larger amount of lower olefin than that when thecombustion temperature T is the first combustion temperature T1 or underor the combustion temperature T is the second combustion temperature T2or over is exhausted from the cylinder.

Accordingly, when the temperature of the catalyst device 2 is lower thanthe activation temperature of the oxidation catalyst immediately afterthe engine starting-up, if an operation in which the combustiontemperature is higher than the first combustion temperature T1 and lowerthan the second combustion temperature T2 is carried out, a large amountof lower olefin is included in the exhaust gas. Even if the HCadsorption device 3 is arranged immediately upstream the catalyst device2 and a part of the large amount of lower olefin is adsorbed in the HCadsorption device 3, a relative large amount of lower olefin obstructsthe oxidation of CO in the oxidation catalyst and thus drops theoxidation rate of CO so much.

Therefore, the warming-up of the catalyst device 2 using the oxidationreaction heat of CO becomes insufficiently and thus the quick warming-upof the catalyst device cannot be realized. If the HC adsorption device 3is not arranged upstream the catalyst device, when the operation inwhich the combustion temperature is higher than the first combustiontemperature T1 and lower than the second combustion temperature T2 iscarried out, a large amount of lower olefin extremely drops theoxidation rate of CO so as to delay the warming-up of the catalystdevice 2 more.

The control system of the present embodiment controls the engineaccording to a first flow-chart shown in FIG. 4 to realize the quickwarming-up of the catalyst device 2. First, at step 101, it isdetermined if the temperature (t) (measured or estimated) of thecatalyst device 2 is lower than a set temperature (t′) (for example, theactivation temperature of the oxidation catalyst). When the result atstep 101 is negative, the warming-up of the catalyst device 2 hasfinished, and therefore at step 102, regular combustion is carried out.

On the other hand, when the result at step 101 is positive, thewarming-up of the catalyst device 2 has not finished, and therefore atstep 103, combustion for restraining the production of lower olefin iscarried out. In the combustion for restraining the production of lowerolefin, the combustion temperature T (maximum combustion temperature) inthe cylinder is made the first combustion temperature T1 or under, orthe second combustion temperature T2 or over.

For example, when an exhaust valve open timing can be varied by avariable valve timing mechanism, if the exhaust valve open timing isadvanced to bring forward the combustion finishing time in an expansionstroke, the combustion temperature can be made the first combustiontemperature T1 or under. On the other hand, if the exhaust valve opentiming is delayed to bring backward the combustion finishing time in anexpansion stroke, the combustion temperature can be made the secondcombustion temperature T2 or over. Further, an addition fuel injectioninto the cylinder in an expansion stroke can make the combustiontemperature the second combustion temperature T2 or over.

When the maximum combustion temperature T is made the second combustiontemperature T2 or over, there is a period in which the temperature inthe cylinder is higher than the first combustion temperature T1 and islower than the second combustion temperature T2. However, this period isvery short and may not contribute to the production of lower olefin.

Thus, according to the combustion for restraining the production oflower olefin, an amount of exhausted lower olefin which extremely dropsthe oxidation rate of CO in the oxidation catalyst can be decreased sothat the oxidation rate of CO in the oxidation catalyst is increased soas to realize the quick warming-up of the catalyst device 2 by theoxidation reaction heat of CO.

FIG. 5 is a second flow-chart showing a control of the engine carriedout by the control system of the present embodiment, to realize thequick warming-up of the catalyst device 2. First, at step 201, it isdetermined if the temperature (t) (measured or estimated) of thecatalyst device 2 is lower than the set temperature (t′) (for example,the activation temperature of the oxidation catalyst). When the resultat step 201 is negative, the warming-up of the catalyst device 2 hasbeen finished and therefore at step 202, a demanded operation is carriedout as it is.

On the other hand, when the result at step 201 is positive, at step 203,a current combustion level is determined on the basis of fuel propertiesin the fuel tank (for example, cetane number and a concentration ofsulfur), parts deterioration degree (for example, deterioration degreesof the fuel injector and the recirculation exhaust gas cooler), and thelike. Next, at step 204, an area A in which an engine operation isprohibited is determined on the basis of the current combustion level.

The area A in which an engine operation is prohibited is shown in FIG.6, and is an operation area in which the combustion temperature T(maximum combustion temperature) becomes higher than the firstcombustion temperature T1 and lower than the second combustiontemperature T2. The more the combustion level deteriorates, the higherthe engine load in which the combustion temperature is low becomes.Therefore, the area A in which an engine operation is prohibited expandsto the high engine load side. Namely, the solid line is the area inwhich an engine operation is prohibited when the combustiondeterioration level is low. The dotted line is the area in which anengine operation is prohibited when the combustion deterioration levelis middle. The chain line is the area in which an engine operation isprohibited when the combustion deterioration level is high.

Next, at step 205, it is determined if the current demanded operation isin the area A in which an engine operation is prohibited determined atstep 204. When the result at step 205 is negative, at step 206, thedemanded operation out of the area A in which an engine operation isprohibited is carried out as it is.

On the other hand, when the result at step 205 is positive, at step 207,an engine load control is carried out so that the operation out of thearea A in which an engine operation is prohibited can be carried out atstep 206. For example, the engine load control makes an alternator loadincrease to increase a demanded load of the engine. Therefore, thedemanded engine operation can be made out of the area A in which anengine operation is prohibited.

Further, for example, when the engine is used in a hybrid vehicle, theengine load control can make a motor-generator operates as a generator,can make an amount of power generated by the motor-generator operatingas a generator increase, or can make a torque generated by themotor-generator operating as a motor decrease, in order to increase ademanded load of the engine. Therefore, the demanded engine operationcan be made out of the area A in which an engine operation isprohibited.

Further, the engine load control can make an amount of power generatedby the motor-generator operating as the generator decrease, can make themotor-generator operate as the motor, or can make a torque generated bythe motor-generator operating as the motor increase, in order todecrease a demanded load of the engine. Therefore, the demanded engineoperation can be made out of the area A in which an engine operation isprohibited.

Thus, when the warming-up of the catalyst device 2 has not beenfinished, an operation exhausting a large amount of lower olefin isprohibited so that an amount of exhausted lower olefin which makes theoxidation rate of CO in the oxidation catalyst extremely decrease can bereduced. Therefore, the oxidation rate of CO in the oxidation catalystcan be increased to realize the quick warming-up of the catalyst device2 by using of the oxidation reaction heat of CO.

In the present embodiment, HC adsorption device 3 is arrangedimmediately upstream the catalyst device 2 having the oxidation ability.However, this does not limit the present invention. Even if the HCadsorption device 3 is omitted, it is advantageous for the quickwarming-up of the catalyst device 2 to reduce an amount of exhaustedlower olefin before finishing the warming-up of the catalyst device 2.

LIST OF REFERENCE NUMERALS

1: exhaust passage

2: catalyst device

3: HC adsorption device

1. A control system of an internal combustion engine in which a catalystdevice having the oxidation ability is arranged in the exhaust system,wherein when a temperature of said catalyst device is lower than a settemperature, the combustion temperature is made a first combustiontemperature or under or is made a second combustion temperature or over,to make an amount of lower olefin in the exhaust gas smaller than thatwhen the combustion temperature is higher than said first combustiontemperature and is lower than said second combustion temperature.
 2. Acontrol system of an internal combustion engine according to claim 1,wherein an engine operating area in which the combustion temperaturebecomes higher than said first combustion temperature and lower thansaid second combustion temperature is set, and when the temperature ofsaid catalyst device is lower than the set temperature, it is prohibitedthat the engine operates in said engine operating area.
 3. A controlsystem of an internal combustion engine according to claim 2, whereinthe worse the combustion becomes, the more said engine operating area isexpanded to the high engine load side.